Initial ambulatory electrocardiographic data from this laboratory has characterized the normal heart rhythm patterns in healthy elderly subjects. We have extended these efforts to include younger men and women (ages 25-60). In addition, we have added a new dimension - 24 hour ambulatory blood pressure (BP) recording - simultaneous with the ambulatory ECG recording, in normal subjects as well as hypertensives and those with congestive heart failure. We have analyzed the circadian variability of blood pressure, recorded every 7.5 min, over 24 hours in 26 healthy normotensive BLSA women ages 35-75 years using this technique. Both the mean waking systolic blood pressure (SBP) and its standard deviation increased with age whereas during sleep, he mean SBP but not its standard deviation increased with age. The difference between maximum and minimum hourly-averaged waking SBP increased with age whereas the difference during sleep was not age-related. Thus, in ambulatory, normotensive women, the variability of SBP increased with age during waking hours but not during sleep.